What was the real size of the British Empire at its peak?

The British Empire reached its greatest territorial extent in the aftermath of World War I.

By 1920, it covered approximately 35.5 million square kilometers (about 13.7 million square miles) of land – roughly 24% of the Earth's total land area.

This made it the largest empire ever, significantly larger than any other empire in history.

For perspective, the British realm in 1920 was almost half again as large as the next-largest empire (the Mongol Empire), which had covered about 24 million km² at its peak.

Major components of the British Empire at its height included the Dominions (such as Canada, Australia, New Zealand, and South Africa), crown colonies across Africa (from Egypt and Sudan to South Africa and numerous West African territories), British India (which included modern India, Pakistan, Bangladesh, Burma/Myanmar, etc.), parts of the Middle East (Palestine, Iraq, etc. under League of Nations mandates), virtually all of present-day Oceania (e.g. Malaya, Singapore, Hong Kong in Asia; Fiji and other Pacific islands), and numerous islands and enclaves in the Caribbean and Americas.

Such was its global sprawl that British territories encircled the planet. 

Britain’s rise as a colonial power began in the 17th century, accelerating after it defeated rival European powers like the Netherlands and France in a series of 18th-century colonial wars.

A key turning point was the Napoleonic Wars (1803–1815): after defeating Napoleonic France, Britain emerged with unrivaled naval supremacy and grabbed key colonies.

Throughout the 1800s, Britain also expanded its holdings via the “Scramble for Africa”, and extended its influence in Asia, most notably in India and Malaya. 

By 1913, the British Empire governed roughly 412 million people, about 23% of the world’s population at that time.

This means nearly one in four people on Earth lived under some form of British imperial authority.

The largest share of these subjects lived in British India, which was the empire’s demographic and economic heartland.  As a result, it was often called the "jewel in the crown".

Hundreds of millions in India and the rest of South Asia were under British rule, alongside tens of millions in Africa (e.g. Nigeria, Egypt, South Africa), Southeast Asia (Malaya, Burma), and smaller numbers in colonies or dominions with significant European settlement (Canada, Australia, etc.). 

It’s worth noting that the imperial population continued to grow into the mid-20th century due to natural increase and the addition of new territories after World War I.

By the eve of World War II, the British Empire is estimated to have ruled over 500–600 million people, and just after WWII the figure may have reached as high as 700 million before large-scale decolonization began. 

Britain was the first nation to industrialize, and by the mid-19th century it had become the “workshop of the world”.

As a result of the Industrial Revolution, which began in Britain in the late 18th century, Britain became the wealthiest country in the world by the 19th century and enjoyed unparalleled manufacturing and financial might.

During the Pax Britannica (c. 1815–1914), when British naval power ensured relative global peace, the Empire not only controlled its formal colonies but also dominated international commerce.

In this era, Britain’s dominance of world trade and the oceans meant it could effectively control the economies of many regions even outside its empire.

London became the globe’s leading financial center, and Britain was the leading exporter of capital. 

By 1870, the British Empire had achieved a remarkable economic pinnacle: it was the world’s largest economy by nominal GDP and accounted for an estimated one-quarter of global trade.

In other words, about 25% of all world commerce at that time was British-controlled, which was a staggering figure.

British exports and imports circled the world along the sea lanes protected by the Royal Navy.

Trade was so crucial that it made up roughly one-third of Britain’s own GDP in the 19th century.

Britain’s industrial output was unmatched for decades; for example, one estimate suggests that around 1870 Britain alone produced about 30% of the world’s industrial output.

Even as late as 1913, on the eve of World War I, the homelands of Britain alone still accounted for about 27% of the world’s manufacturing exports in textiles, steel, machinery, and other goods.

The empire’s vast resources and markets helped, as colonies provided raw materials and were outlets for British manufactured products. 

However, by the early 20th century Britain’s relative lead was starting to narrow as other powers industrialized.

The United States and Germany emerged as major industrial economies. However, Britain remained a huge economic force, but its economy was eventually surpassed by the United States around World War I (circa 1916).

Even so, no other nation at the time had the same global economic reach: the British pound sterling was effectively the world currency, London’s banks financed international projects, and British merchant ships carried a large share of world trade.

In 1870 about 25% of all global trade was British, and even in 1914 Britain’s share of world trade and investments was enormous.

This trade influence was bolstered by Britain’s advocacy of free trade in the 19th century, after the repeal of protectionist laws, and Britain embraced near-unrestricted trade.

This, combined with its naval supremacy, allowed British merchants to penetrate markets on every continent. 

Therefore, at Britain’s imperial peak, no single rival combined the same territorial scope, population, and economic clout.

The French and Russian Empires were substantial but smaller and less globally integrated; emergent powers like the U.S. and Germany rivaled Britain economically by the 20th century but not in colonial reach.

This unique combination of advantages left Britain as the pre-eminent superpower of the 19th century.

The long-term significance of this era is still obvious in the widespread use of the English language, as well as the common legal and government frameworks in former colonies, and global trade networks that Britain helped establish.